I am new to ELISA and I need help in the formulation of a wash buffer. There are several components to the creation of this buffer, however what I am having trouble with is diluting a stock solution of (Na2HPO4*7H2O) to the desired reagent (Na2HPO4*12H2O). This buffer requires 2.9 g of Na2HPO4*12H2O. I am mainly unsure of whether this adjustment is necessary? Since the reagent will be dissolved in water to create the buffer.
I would greatly appreciate any help!
Hi Peter,
calculate the moles of the NaHPO4 variety stated in the recipe (the 7 H20 variety) and correct for the molar mass of what is available to you (the 10 H20 variety). In your specific case, the correction factor is M(Na2HPO4x10H20)/M(Na2HPO4x7H2O). M refers to the molar masses. Calculate, ask e.g. Wikipedia or have a look into a supplier's catalogue.
BTW, this is not ELISA specific, but simple general chemistry.
Dear Peter Foerster ,
First of all you are dealing with two examples of different hydrate forms of diphosphates. It is ‘just’ the same disodium hydrogen phosphate with the formula Na2HPO4· nH2O were n is in your case either 7 or 12. Hydrates of (inorganic) salts are those salts that containing water molecules in a definite ratio with the water molecules built in as an integral part of the crystal. So this is only relevant in solid state, once dissolved in water there is no distinction.
Knowing the molar mass:
Na2HPO4.7H2O Molar mass 268.07 g/mol
Na2HPO4.12H2O Molar mass 358.14 g/mol
It is pretty straightforward. If you need a 1 M solution and you have Na2HPO4.7H2O you dissolve 268.07 gram in 1 L, if you have Na2HPO4.12H2O you dissolve 358,14 g/mol.
If your buffer requires 2.9 g of Na2HPO4*12H2O you just need, asbasically explained by Wolfgang Schechinger , 268.07/358.14 * 2.9 gram Na2HPO4.7H2O (so 2.17 gram).
Hope this is somewhat more clear to you.
Best regards.
Rob Keller Wolfgang Schechinger Thank you both for your help! It clears it up so much. The general chemistry of it was indeed straightforward, but I had trouble with what will happen to the hydrate once dissolved in water.
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